1. Field of the Invention
This invention relates to a communication method, a transmitting method, a receiving method, and a base station and terminal devices based on these methods, and more particularly, is applicable to a case where the time division multiplex access (TDMA) method is used.
2. Description of the Related Art
Various wireless telephone systems for wireless transmitting a signal converted into digital data have been put to a practical use. A system to which the TDMA method is applied has been put to a practical use as one of the methods of access efficiently. This method sections one transmission band (frequency channel) by time axis to form time slots and assigns each time slot to a plurality of terminal devices, so that a plurality of terminal devices can access to a base station with one transmission band.
FIG. 1 is a diagram showing an example of the channel construction of a down circuit, through which a signal is transmitted from th e base station to the terminal device, in the conventional wireless telephone system of the cellular system to which the TDMA method is applied. The ordinate represents frequency and the abscissa represents the passage of time. The frequency axis forms one band slot for each predetermined frequency band (e.g., for each several KHz), each having band slot number (consecutive number). The time axis forms one time slot for each predetermined time (e.g., for each several hundred xcexc sec. each having time slot number (consecutive number).
In FIG. 1, sixteen band slots are set as a transmission band controlled by one control channel, and a band slot for common control channel CCH is assigned to the first band slot of sixteen band slots, and the seventeenth band slot___. In the band slot for control channel CCH, all time slots are only used for control channel.
Then, fifteen band slots following each control channel (e.g., the second to sixteenth band slots) are set to a transmission band for traffic channel TCH which transmits voice for telephone call or various data. The setting of the traffic channel TCH in the transmission band is informed from the base station to each terminal device through the control channel. Accordingly, in the case of accessing to the base station, each terminal device firstly receives the band slot in which the control channel CCH is transmitted to determine the band slot and time slot assigned to the terminal device from the control information designated by the control channel CCH transmitted in this band slot, and starts to communicate with the base station in the band slot and time slot.
For example, in the case of dividing one band slot (frequency channel) into four to communicate with four terminal devices, each terminal device communicates at a period of four time slots (in the case of using another band for an up circuit). The communication of one terminal device is shown in FIG. 8. Here, the time slot numbers of the fourth band slot 1, 5, 9, 13, . . . are used to communicate with the base station in the traffic channel TCH.
The wireless communication applying the TDMA method is performed in this way. However, it is a basic that the frequency channel assigned to the control channel CCH does not have the interference wave within the base station area (cell). Accordingly, it had been difficult to use the frequency of the control channel in common with the base station of adjacent cell, since the signal of control channel becomes jammed between base stations.
When the time slot period is synchronous between base stations by some methods, the time slot period in the band slot used as the control channel CCH is divided and used with the adjacent base station, so as to use the frequency channel for control channel in common between base stations. However, in order to synchronize the base stations with each other, it is needed that some synchronous data is transmitted between base stations or some standard signal (such as a position detecting signal for GPS) is received at each base station to perform the synchronization processing. There is a problem that the construction of the base station and the processing become complicated.
Further, in the wireless telephone system, when the frequency channel used as the control channel is a fixed channel, the communication may not be in favorable conditions depending on the condition of transmission path at that time since the position of the terminal device is not fixed. To avoid this problem, a plurality of frequency channels are used for the control channel, so as to obtain the frequency diversity effect and strong possibility of favorable communication. However, if a plurality of frequencies for control channel are prepared in the conventional system construction shown in FIG. 8, the frequency channel which can be used as the traffic channel TCH decreases and this is not favorable.
In view of the foregoing, an object of this invention is to efficiently set a control channel in each base station.
The foregoing object and other objects of the invention have been achieved by the provision of a communication method of forming time slots by sectioning time into every predetermined period of time and communicating between a base station and an arbitrary number of terminal devices intermittently with a predetermined number of time slot period, wherein a frequency channel for communication changes into a predetermined state in a time slot unit. The communication method comprises the steps of: providing a channel group for control information communication as a channel for transmitting from the base station, in addition to channels for information communication to communicate with the terminal devices; fixing the frequency channel, where an initial acquisition channel exists, of the channel group for control information communication to a predetermined frequency channel; in the frequency channel assigned to the initial acquisition channel, setting a time slot in which the initial acquisition information is transmitted by a predetermined random number sequence, and storing the set random number information in the initial acquisition information to be transmitted; and determining the time slot in which the initial acquisition channel is transmitted, based on the random number obtained by receiving at the terminal devices the frequency channel where the initial acquisition channel exists.
Further, this invention provides a transmitting method of forming time slots by sectioning time into every predetermined period of time and transmitting intermittently with a predetermined number of time slot period, wherein a frequency channel for transmission changes into a predetermined state in a time slot unit. The transmitting method comprises the steps of: providing a channel group for control information transmission as a channel for transmission, in addition to channels for information transmission; fixing the frequency channel, where an initial acquisition channel exists, of the channel group for control information transmission to a predetermined frequency channel; and in the frequency channel assigned to the initial acquisition channel, setting a time slot in which the initial acquisition information is transmitted by a predetermined random number sequence, and storing the set random number information in the initial acquisition information to be transmitted.
Further, this invention provides a receiving method of forming time slots by sectioning time into predetermined period of time and receiving intermittently with a predetermined number of time slot period, wherein a frequency channel for reception changes into a predetermined state in a time slot unit. The receiving method comprises the steps of: providing a channel group for control information reception as a channel for reception, in addition to channels for information reception; receiving the frequency channel, where the initial acquisition channel exists, of the channel group for control information reception by the predetermined frequency channel; and determining the time slot in which the initial acquisition channel is transmitted, by the random number included in the received frequency channel.
Further, this invention provides a base station for forming time slots by sectioning time into predetermined period of time and communicating with terminal devices intermittently with a predetermined number of time slot period, and for performing the frequency hopping that the frequency channel for communication changes into a predetermined state in a time slot unit. In the base station, processing means of a channel for information communication and processing means of a channel for control information communication are provided; an initial acquisition channel and a broadcast channel are provided as a channel group for control information communication which is transmitted by the processing means of a channel for control information communication; the initial acquisition channel is fixed to a predetermined frequency channel and transmitted; and in the frequency channel where the initial acquisition channel exists, the time slot in which the initial acquisition information is transmitted is set by a predetermined random number sequence generated by the processing means of a channel for control information communication, and the set random number information is stored in the initial acquisition information to be transmitted.
Further, this invention provides a terminal device of forming time slots by sectioning time into predetermined period of time and communicating intermittently with a predetermined number of time slot period, and of performing the frequency hopping so that the frequency channel for communication changes into a predetermined state in a time slot unit. In the terminal device, processing means of a channel for information communication and processing means of a channel for control information communication are provided; the frequency channel, where the initial acquisition channel exists, of the channel group for control information reception received by the processing means of a channel for control information communication is received in a predetermined frequency channel; and the time slot in which the initial acquisition information is transmitted is determined by the random number information included in the received frequency channel, and the time slot is received by the processing means of a channel for control information communication.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.